In the field of graphic arts, a system for forming an image having a photographic characteristic of ultrahigh contrast (especially .gamma. of 10 or more) is required for enabling reproduction of a continuous resolution image through a half-tone image or reproduction of a line original image.
As a process for obtaining photographic characteristics of high contrast image, a lith developing method utilizing what is called an "infectious developing effect" has been used for a long time, but it has the disadvantage that the developer is unstable and, thus, it is difficult to be used.
On the other hand, processes for obtaining a high contrast image using a more stable developer are disclosed in, for example, U.S. Pat. Nos. 4,224,401, 4,168,977, 4,166,742, 4,311,781, 4,272,606, 4,221,857, 4,332,878, 4,634,661, 4,618,574, 4,269,922, 5,650,746, and 4,681,836.
These image forming systems are those in which a hydrazine derivative-added surface latent image type silver halide photographic material is processed with a stable MQ developer (a developer containing hydroquinone and p-aminophenols in combination) or PQ developer (a developer containing hydroquinone and 1-phenyl-3-pyrazolidones in combination) having a pH value of from 11 to 12.3 to obtain an ultrahigh contrast negative image having a .gamma. value exceeding 10. According to these processes, because photographic characteristics of ultrahigh contrast and high sensitivity are obtained and a sulfite can be added to a developer in a high concentration, the stability of the developer to air oxidation is markedly improved in comparison with the conventional lith developer.
With regard to a photographic material for light room developing, which is used in assembly processes and dot-to-dot working operations, for example, in the case where the superimposition dot-to-dot working operation between a half-tone dot text and line original text is attempted to be carried out faithfully to the texts, a process for forming an image having an ultrahigh contrast is required. For this purpose, the above-mentioned image forming systems using a hydrazine derivative are effective, and the typical application examples are disclosed in JP-A-62-640 (the term "JP-A" used herein means an "unexamined published Japanese patent application"), JP-A-62-235938, JP-A-62-235939, JP-A-63-104046, JP-A-63-103235, JP-A-63-296031, JP-A-63-314541, and JP-A-64-13545.
U.S. Pat. Nos. 4,998,604 and 4,994,365 disclose a hydrazine compound having ethylene oxide repeating units and a hydrazine compound having a pyridinium group. However, as is clear from examples described therein, the high contrast is not yet sufficient, and it is difficult to obtain a high contrast and a necessary D.sub.max value under the practical developing conditions.
On the other hand, it has been known that endiols such as ascorbic acid can function as the main developing agent, and they attracted the attention as the main developing agent having no problem in terms of ecology and toxicology. For example, U.S. Pat. Nos. 2,688,549 and 3,826,654 disclose that images can be formed under a strong alkaline condition of a pH of 12 or more. However, no high contrast image can be obtained in these image forming processes.
Several attempts have been made to increase the contrast in the developing system using ascorbic acid. For example, Zwicky discloses that in the case of using ascorbic acid as a sole main developing agent, a type of lith effect is expressed (J. Phot. Sc. Vol. 27, p. 185 (1979)), but the system using ascorbic acid has a low contrast in comparison with a hydroquinone-containing system. U.S. Pat. No. 1,896,022 and JP-B-49-46939 (the term "JP-B" used herein means an "examined Japanese patent publication") disclose a system using a bisquaternary ammonium salt and ascorbic acid in combination, but even though the system has a developing acceleration effect, it has little effect for increasing contrast. JP-A-3-249756 and JP-A-4-32838 also disclose the combination effect of use of ascorbic acid and a quaternary salt, but the resultant images have insufficient contrast. Furthermore, according to JP-A-5-88306, a high contrast can be obtained by using ascorbic acid as a sole developing agent and keeping the pH at 12.0 or more, but this system has a problem in terms of stability of the developer.
U.S. Pat. No. 3,730,727 discloses an example where a special developer comprising ascorbic acid and a hydrazine derivative as main ingredients can be used to obtain a developed system having a high sensitivity and low stain and fogging, but does not disclose enhancement of contrast.
It has been known that a photographic material containing hydrazine is processed with an ascorbic acid developer, and it is disclosed in, for example, U.S. Pat. No. 5,236,816, and WO 93/11456. In each case, a sufficient contrast cannot be obtained. Additionally, in WO 93/11456, although a high contrast is obtained by incorporating an amine compound into a developer, it is not preferable in terms of environment. A development processing method to obtain a high contrast image by using an ascorbic acid developing agent, which is preferred in terms of toxicology, has been desired. However, a sufficient contrast has not been obtained. Furthermore, if an ascorbic acid developing agent is used, the pH is greatly lowered because of air oxidation, and as a result, there have been practical problems because the photographic properties are greatly lowered. In addition, because high contrast images for a printing film are obtained by processing the light-sensitive material with a developer having a relatively high pH of 11 or more, stability for air oxidation in these methods is insufficient.